Micro-fluid ejection assemblies typically include a silicon substrate material that contains fluid openings, trenches, and/or depressions formed therein. The fluid openings, trenches, and/or depressions are collectively referred to herein as “flow features.” Such flow features may be formed by a wide variety of micromachining techniques including sand blasting, wet chemical etching and reactive ion etching. As the devices become smaller, such as for ink jet printhead applications, micromachining of the substrates becomes a more critical operation. Not all micromachining techniques are reliable enough to produce accurately placed flow features having similar flow characteristics in the substrates. Accordingly, the micro-fluid ejection assembly art is constantly searching for improved micro-fluid ejection assemblies that can be produced in high yield at a minimum cost.
One method for micromachining silicon substrates is a dry etching process such as deep reactive ion etching (DRIE) or inductively coupled plasma etching. When dry etching a silicon substrate, parameters that are beneficial to one characteristic of the etched substrate are sometimes detrimental to another characteristic of the substrate.
For example, with reference to the prior art figures of FIGS. 1-3, silicon substrates 10 having fluid supply slots 12 therein require the fluid slots 12 to have a reentrant configuration for proper fluid flow as shown in FIG. 1. However, providing reentrant configurations for the fluid supply slots may cause top side silicon 10 damage 14 as shown in FIG. 2 and undercutting of a planarization layer 16 as shown in FIG. 3. Such top side silicon damage 14 may negatively affect shelf length control, which may lead to cross-talk, low chip strength and performance variability. Undercutting of the planarization layer 16 may lead to unwanted fluid intrusion between the silicon 10 and the planarization layer 16 on the silicon as shown in FIG. 3 which may cause the planarization layer 16 to delaminate from the substrate 10.
Accordingly, there remains a need for improved structures and methods of forming fluid supply slots in a semiconductor substrate using an improved wet or dry etch process.